* {
    padding: 0;
    margin: 0;
}

html {
    font-size: 62.5%;
    font-family: "Microsoft YaHei", sans-serif;
}

body {
    text-align: left;
    background-color: #424242;
    font-size: 1.4rem;
}

body > header {
    height: 4.4rem;
    line-height: 4.4rem;
    background-color: rgba(0,0,0,0.2);
}

.theme {
    color: #2196F3;
    transition: all 2s ease;
}

#logo {
    padding-left: 2.4rem;
    font-size: 1.25em;
}

.container {
    margin: 2.4rem auto;
    max-width: 60rem;
    border-radius: 1.6rem;
    overflow: hidden;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.4);
}

.container>header {
    height: 4rem;
    line-height: 4rem;
    position: relative;
    text-align: center;
    overflow: hidden;
}

#indicator {
    height: 0.6rem;
    background-color: #CDDC39;
    width: 25%;
    position: absolute;
    left: 0;
    top: 0;
}

#content {
    display: flex;
    flex-flow: row wrap;
    align-items: center;
    justify-content: flex-start;
    padding: 1.6rem;
}

.card {
    background: #fafafa;
    flex: 1 1 16.7%;
    margin: 1.6rem;
    border-radius: 0.8rem;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.4);
    overflow: hidden;
}

.card:after {
    content: '';
    padding-top: 100%;
    display: block;
}

.card img {
    float: left;
}

.fa {
    margin: 0 0.8rem;
    font-size: 1.25em;
}

nav {
    float: left;
    width: 25%;
    cursor: pointer;
    color: #bdbdbd;
    overflow: hidden;
    background-image: linear-gradient(0deg, rgba(0, 0, 0, 0.4) 95%, rgba(0, 0, 0, 0.3) 100%);
    transition: font 0.2s ease;
}

nav.current {
    background-color: transparent;
    font-size: 1.6rem;
    color: white;
    background-image: none;
    border-radius: 0.4rem 0.4rem 0 0;
    line-height: 5.2rem;
}

.flip {
    animation: flip 0.2s ease;
}

@keyframes flip {
    0% {
        transform: rotate3d(0, 1, 0, 90deg);
    }

    100% {
        transform: rotate3d(0, 1, 0, 360deg);
    }
}